Study On Topology Optimization To Mid-section Structures Of Oil Tankers

In recent years, ship structure optimization design is a hot research topic; the main goal isto reduce the hull structure steel weight under the premise of the structure strength.Topology optimization is different from the general size optimization; it is to find theoptimal structure material distribution form and force transmission path. Until now, theresearch on the ship’s structure optimization is basically forcus on the size optimization,but less studies on topology optimization. On the other hand, the steel weights of large oiltankers designed by China is larger than the similar ones by Japan or Korea. Therefore, itis necessary to optimize the hull structure design to decrease the steel weight. This paperis to optimize the mid-section structure of oil tankers by topology optimization method.(1) According to the element evolution algorithm, one of the topologyoptimization methods, the element stress index and the element weighting coefficient aredefined to create the objective function. The mathematical calculation model of suchoptimization is created by the iteration equation of the element weighting coefficientdetermined by the calculation of the element stress, and the FEM balance equation. Thedetail evolution optimization process is introduced in the optimization to the mid-sectionstructures of a VLCC for crosstieless arrangement.(2) Acoording to the continuum structure topology optimization method, theoptimization variables are the elements’ material density based on the SIMP materialdensity model;, the constraint conditions can be set as the structural static responsecombining with the finite element balance equation; the optimizaion’s objective functionis defined as the volume function, which can promote the efficiency and stability of theoptimization calculating. By introducing the K-T condition to determine the optimizationcriterion, the iteration equation of variables can be created. Thus, the complete topology optimization method is set, whose accuracy is verified by the comparison with theclassical topology optimization algorithm.(3) According to the common structural rules for double hull oil tankers(CSR-OT), the three-dimensional finite element model and its load boundary conditionscan be created.6calculation conditions are determined by the number of longitudinalbulkhead and the load boundary. The established continuum structure topologyoptimization method is used to optimize the mid-section structure of a typical VLCC anda Suezmax tanker.(4) Based on the topology optimization results,3preferable mid-section structuredesign options for a320000DWT VLCC are determined. The yielding and bucklingstrength of hull structures for different design options are checked by coarse-mesh cargohold analysis required by CSR-OT respectively. The final optimal results all meet theRule requirement. At last, the reducing weights of different design options are calculatedand compared.